For example, as disclosed in Patent Literature 1, a centrifugal compressor including a casing that bears a shaft including a plurality of stages of impellers with a radial bearing in between, and includes a suction port sucking working fluid at one end part of the shaft in a longitudinal direction, is known.
The centrifugal compressor disclosed in Patent Literature 1 is directed to prevention of occurrence of burn-in at a portion between the shaft and the radial bearing when ethylene gas at low temperature, for example, −60° C. or lower is compressed. In other words, when the working fluid at low temperature is used, thermal contraction occurs on the casing, in particular, at the one end part of the casing including the suction port, and the thermal contraction makes it difficult to maintain an appropriate value of a clearance between the shaft and the radial bearing. Patent Literature 1 proposes provision of a groove that extends along the longitudinal direction of the shaft in a region that is located at the one end part of the casing and is located on outside of the bearing in a radial direction in order to address the thermal contraction difference.
As disclosed in Patent Literature 1, a non-contact gas seal that is excellent in sealing property and has favorable maintainability is often adopted as a shaft-sealing device to the centrifugal compressor. The gas seal supplies high-pressure seal gas to a fine clearance between seal surfaces to seal a periphery of the shaft, namely, provides shaft-sealing. The gas seal may be applied singularly or combined with a labyrinth seal in some cases.